The present invention relates to an automatic preliminary irradiation apparatus in a transmission electron microscope.
In the transmission electron microscope, a specimen undergoes remarkable injuries when irradiated with an electron beam, making it difficult to view and take a picture of the true aspect or structure of the specimen. When a slice of the specimen or a supporting film therefor is feeble, shrinkage is likely to take place in the region of the specimen irradiated with the electron beam, giving rise to a so-called "drift of specimen" and rupture thereof.
In order to protect a specimen against the drift and the rupture in the course of observation and/or photographing of the image, it is known to irradiate preliminarily the specimen with an electron beam of a low intensity preceding to the viewing and/or photographing, so that the slice of specimen and the supporting film may get familiar with the electron beam to be thereby stabilized, as is discussed in Japanese literature entitled "Electron Microscope Observation Method" editted by Japan Society of Electron Microscopy, p. 90. The preliminary irradiation is manually performed by operator with the aid of a specimen fine-moving device such that the specimen (exposed through a grid hole or mesh) is uniformly and thoroughly irradiated with the electron beam having the intensity decreased sufficiently. More specifically, the preliminary irradiation is started by scanning the specimen initially with the electron beam of a low intensity, and then the intensity of the electron beam is progressibly increased while moving the specimen by means of the fine-moving device every time the beam intensity is increased.
Needless to say, the preliminary irradiation performed manually and repeatedly requires not only high skillful on the part of the operator but also a lot of time and labor.